Scala IDE 4.2-RC2 arrived about two weeks ago and since then a few improvements were made. Especially the new Async Debugger got stronger. If you tried 4.2-RC2 please also try 4.2-RC3 and report back anything that doesn’t work the way it should. See the changelog for an overview of all changes in 4.2-RC3.
This is the third release candidate and if no further blockers are found during the next week or so, it will become the final release.